Roadway warning devices, specifically the roadway warning devices commonly referred to as rumble strips, provide a perceptible noise and warning vibration when automotive vehicles, including both passenger vehicles and trucks, drive over the rumble strips. The noise and vibration is intended to warn the vehicle driver of an approaching condition that requires a lower speed or special attention, such as a work site, construction site, slow speed zone, checkpoint, toll booth, and so on, without alarming the driver and without adversely affecting the stability of the vehicle. Some types of rumble strips are intended to be permanently installed for long-term use, while others are intended to be portable for temporary use at work zones and other applications of relatively short duration.